Hippocampal 5-HT1A Receptor and Spatial Learning and Memory

Effects of an external static EF on the conformational transition of 5-HT1A receptor: A molecular dynamics simulation study

The serotonin receptor subtype 1A (5-HT1AR), one of the G-protein-coupled receptor (GPCR) family, has been implicated in several neurological conditions. Understanding the activation and inactivation mechanism of 5-HT1AR at the molecular level is critical for discovering novel therapeutics in many diseases. Recently there has been a growing appreciation for the role of external electric fields (EFs) in influencing the structure and activity of biomolecules. In this study, we used molecular dynamics (MD) simulations to examine conformational features of active states of 5-HT1AR and investigate the effect of an external static EF with 0.02 V/nm applied on the active state of 5-HT1AR. Our results showed that the active state of 5-HT1AR maintained the native structure, while the EF led to structural modifications in 5-HT1AR, particularly inducing the inward movement of transmembrane helix 6 (TM6). Furthermore, it disturbed the conformational switches associated with activation in the CWxP, DRY, PIF, and NPxxY motifs, consequently predisposing an inclination towards the inactive-like conformation. We also found that the EF led to an overall increase in the dipole moment of 5-HT1AR, encompassing TM6 and pivotal amino acids. The analyses of conformational properties of TM6 showed that the changed secondary structure and decreased solvent exposure occurred upon the EF condition. The interaction of 5-HT1AR with the membrane lipid bilayer was also altered under the EF. Our findings reveal the molecular mechanism underlying the transition of 5-HT1AR conformation induced by external EFs, which offer potential novel insights into the prospect of employing structure-based EF applications for GPCRs.

Benefits of exercise on cognitive impairment in alcohol use disorder following alcohol withdrawal

Although most cognitive impairments induced by prolonged alcohol consumption tend to improve within the initial months of abstinence, there is evidence suggesting certain cognitive deficits may persist. This study aimed to investigate the impact of aerobic exercise on learning and memory in alcohol use disorder (AUD) mice following a period of abstinence from alcohol. We also sought to assess the levels of monoamine neurotransmitters in the hippocampus. To this end, we established an AUD mouse model through a two-bottle choice (sucrose fading mode and normal mode) and chronic intermittent alcohol vapor (combined with intraperitoneal injection) and randomly allocated mice into exercise groups to undergo treadmill training. Learning and memory abilities were assessed through the Morris water maze test and spontaneous activity was evaluated using the open field test. The levels of dopamine, norepinephrine, serotonin, and brain-derived neurotrophic factor in the hippocampus were quantified using enzyme-linked immunoassay (ELISA) kits. The findings reveal that after cessation of alcohol consumption, learning and memory abilities in AUD mice did not completely return to normal levels. The observed enhancement of cognitive functions in AUD mice through aerobic exercise may be attributed to restoring levels of monoamine neurotransmitters in the hippocampus, boosting brain-derived neurotrophic factor (BDNF) concentrations, and facilitating an increase in hippocampal mass. These results offer empirical evidence to support aerobic exercise as a viable therapeutic strategy to alleviate cognitive deficits associated with AUD.

Effects of the suppression of 5-HT1A receptors in the left, right, or bilateral basolateral amygdala on memory consolidation in chronic stress in male rats

The serotonin-1A receptors (5-HT1A) in the two cerebral hemispheres are differentially involved in memory. The distribution of 5-HT1A receptors in the left and right amygdala is different. Furthermore, evidence shows that the 5-HT1A receptors in the left and right amygdala work differently in memory function. The basolateral amygdala (BLA) also regulates hippocampal long-term potentiation (LTP) during stress. However, which BLA structure in each hemisphere underlies such lateralized function is unclear. The present research investigated the possible involvement of 5-HT1A lateralization in the BLA on stress-induced memory impairment. 5-HT1A receptor antagonist (Way-100-635) was injected into the left, right, or bilateral BLA twenty minutes before chronic restraint stress (CRS) for 14 consecutive days. Results indicated that suppression of 5HT1A-receptors in the BLA plays an essential role in reducing the acquisition of passive avoidance in the shuttle box test and spatial memory in the Barnes maze test in the stress animals. This decrease was significant in the CRS animals with left and bilateral suppressed 5HT1A-receptors in the BLA. Field potential recording results showed that the left, right, and bilateral injection of Way-100-635 into the BLA significantly reduced the slope and amplitude of fEPSP in the CA1 area of the hippocampus in stressed rats. No significant difference was observed in neuronal arborization in the CA1 area of the hippocampus. In conclusion, the 5-HT1A receptor in the left and right sides of BLA nuclei play a different role in memory consolidation in the hippocampus under stress.

Serotonergic dysfunction may mediate the relationship between alcohol consumption and Alzheimer's disease

The impact of Alzheimer's disease (AD) and its related dementias is rapidly expanding, and its mitigation remains an urgent social and technical challenge. To date there are no effective treatments or interventions for AD, but recent studies suggest that alcohol consumption is correlated with the risk of developing dementia. In this review, we synthesize data from preclinical, clinical, and epidemiological models to evaluate the combined role of alcohol consumption and serotonergic dysfunction in AD, underscoring the need for further research on this topic. We first discuss the limitations inherent to current data-collection methods, and how neuropsychiatric symptoms common among AD, alcohol use disorder, and serotonergic dysfunction may mask their co-occurrence. We additionally describe how excess alcohol consumption may accelerate the development of AD via direct effects on serotonergic function, and we explore the roles of neuroinflammation and proteostasis in mediating the relationship between serotonin, alcohol consumption, and AD. Lastly, we argue for a shift in current research to disentangle the pathogenic effects of alcohol on early-affected brainstem structures in AD.

Insights into the development of 99mTc-radioligands for serotonergic receptors imaging: Synthesis, labeling, In vitro, and In vivo studies

Serotonergic (5-hydroxytryptamine; 5-HT) receptors play critical roles in neurological and psychological disorders such as schizophrenia, anxiety, depression, and Alzheimer's diseases. Therefore, it is particularly important to develop novel radioligands or modify the existing ones to identify the serotonergic receptors involved in psychiatric disorders. Among the 16 subtypes of serotonergic systems, only technetium-99m based radiopharmaceuticals have been evaluated for serotonin-1A (5-HT1A), serotonin-2A (5-HT2A), 5-HT1A/7 heterodimers and serotonin receptor neurotransmitter (SERT). This review focuses on recent efforts in the design, synthesis and evaluation of 99mTc-radioligands used for single photon emission computerized tomography (SPECT) imaging of serotonergic (5-HT) receptors. Additionally, the discussion will cover aspects such as chemical structure, in vitro/vivo stability, affinity toward serotonin receptors, blood-brain barrier permeation (BBB), and biodistribution study.

Transcriptomics and biochemical evidence of trigonelline ameliorating learning and memory decline in the senescence-accelerated mouse prone 8 (SAMP8) model by suppressing proinflammatory cytokines and elevating neurotransmitter release

In recent years, exploring natural compounds with functional properties to ameliorate aging-associated cognitive decline has become a research priority to ensure healthy aging. In the present study, we investigated the effects of Trigonelline (TG), a plant alkaloid, on memory and spatial learning in 16-week-old senescence-accelerated mouse model SAMP8 using an integrated approach for cognitive and molecular biology aspects. After 30 days of oral administration of TG at the dose of 5 mg/kg/day, the mice were trained in Morris Water Maze task. TG-treated SAMP8 mice exhibited significant improvement in the parameters of escape latency, distance moved, and annulus crossing index. Next, we performed a whole-genome transcriptome profiling of the mouse hippocampus using microarrays. Gene ontology analyses showed that a wide range of biological processes, including nervous system development, mitochondrial function, ATP synthesis, and several signaling pathways related to inflammation, autophagy, and neurotransmitter release, were significantly enriched in TG-treated SAMP8 compared to nontreated. Further, a nonlinear dimensionality reduction technique, Uniform Manifold Approximation and Projection (UMAP), was applied to identify clusters of functions that revealed TG primarily regulated pathways related to inflammation, followed by those involved in neurotransmitter release. In addition, a protein-protein interaction network analysis indicated that TG may exert its biological effects through negatively modulating Traf6-mediated NF-κB activation. Finally, ELISA test showed that TG treatment significantly decreased proinflammatory cytokines- TNFα and IL6 and increased neurotransmitters- dopamine, noradrenaline, and serotonin in mouse hippocampus. Altogether, our integrated bio-cognitive approach highlights the potential of TG in alleviating age-related memory and spatial impairment.

Cannabidiol exhibits anxiolytic-like effects and antipsychotic-like effects in mice models

Cannabidiol (CBD), a non-psychoactive compound derived from the cannabis plant, has been confirmed to induce anxiolytic-like and antipsychotic-like effects. However, the exact mechanisms remain unclear. This study substantiated CBD's interaction with the 5-HT1A receptor (5-HT1AR) in vitro (CHO cells expressing human 5-HT1AR) and in vivo (rat lower lip retraction test, LLR test). We then assessed the impact of CBD in mice using the stress-induced hyperthermia (SIH) model and the phencyclidine (PCP)-induced negative symptoms of schizophrenia model, respectively. Concurrently, we investigated whether WAY-100635, a typical 5-HT1AR antagonist, could attenuate these effects. Furthermore, the neurotransmitter changes through high-performance liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) were studied. Results revealed that CBD exhibits selective 5-HT1AR agonists-mediated effects in the rat lower lip retraction test, aligning with the robust agonistic (EC50 = 1.75 μM) profile observed in CHO cells. CBD at 3 mg/kg significantly reduced SIH (ΔT), a response that WAY-100635 abolished. Chronic administration of CBD at 100 mg/kg mitigated the increase in PCP-induced immobility time in the forced swim test (FST) and tail suspension test (TST). Moreover, it induced significant alterations in gamma-aminobutyric acid (GABA) and norepinephrine (NE) levels within the hippocampus (HPC). Thus, we concluded that the 5-HT1AR mediates CBD's anxiolytic-like effects. Additionally, CBD's effects on the negative symptoms of schizophrenia may be linked to changes in GABA and NE levels in the hippocampus. These findings offer novel insights for advancing the exploration of CBD's anxiolytic-like and antipsychotic-like effects.

Fermented mixed grain ameliorates chronic stress-induced depression-like behavior and memory deficit

Fermented mixed grain (FG) has beneficial anti-cancer, antioxidant, and anti-inflammatory effects. In this study, we investigated the effects of FG on gut inflammation, brain dysfunction, and anxiety/depression-like behavior induced by unpredictable chronic mild stress (UCMS) in mice. Mice were administered mixed grain or FG for 3 weeks and were then exposed to UCMS for 4 weeks. FG administration ameliorated stress-induced anxiety/despair-like behavior. FG administration also prevented UCMS-induced memory impairment. Additionally, the mRNA levels of 5-HTR1A and IL-6 were restored to normal levels in the brains of FG-administered mice. FG administration also inhibited intestinal damage in stressed mice compared with that in the UCMS (without FG) group. These results suggest that FG can alleviate stress-induced intestinal damage, brain dysfunction, and cognitive impairment.

Serotonergic neurotransmission mediated cognitive dysfunction in two mouse models of sepsis-associated encephalopathy

BACKGROUND

Patients with sepsis-associated encephalopathy (SAE) often exhibit cognitive impairments. Despite this, the underlying mechanisms of SAE remain largely unexplored. Here, we explored the role of serotonergic neurotransmission in cognitive dysfunction of two mouse models of SAE.

METHODS

The mouse models of SAE were established by injection of lipopolysaccharide (LPS, 10 mg/kg, intraperitoneal) and cecal ligation puncture (CLP) respectively. Barnes maze, new object recognition test and open field test were used to evaluate the effects of fluoxetine (selective serotonin reuptake inhibitor) and cyproheptadine (nonselective 5-HT2 receptor antagonist) on cognition and motor activity of mice. Additionally, WAY100635 (5-HT1A receptor antagonist) was co-administered with fluoxetine to explore the mechanism underlying effect of fluoxetine on cognitive impairments of SAE. Enzyme-linked immunosorbent assay (ELISA) was performed to determine 5-HT levels in hippocampus, brainstem and frontal lobe of experimental groups.

RESULTS

Both LPS-induced sepsis and CLP induced sepsis resulted in a notable learning deficit. Fluoxetine ameliorated, while cyproheptadine aggravated, cognitive impairment in two classic mouse models of SAE. The cognition-enhancing effect of fluoxetine is reversed by WAY100635. Decreased 5-HT levels in hippocampus, brainstem and frontal lobe were observed in LPS septic model and CLP septic model. Notably, both fluoxetine and cyproheptadine significantly increased 5-HT levels in those brain regions in LPS septic model. Additionally, fluoxetine significantly increased 5-HT levels in frontal lobe of CLP septic model.

CONCLUSIONS

Our study demonstrated that serotonergic neurotransmission plays a significant role in mechanisms underlying cognitive impairment in SAE. These findings contribute to identification of novel targets to prevent and arrest cognitive impairment in SAE.

The brain serotonin system in autism

Autism spectrum disorders (ASDs) are among the most common neurodevelopmental diseases. These disorders are characterized by lack of social interaction, by repetitive behavior, and often anxiety and learning disabilities. The brain serotonin (5-HT) system is known to be crucially implicated in a wide range of physiological functions and in the control of different kinds of normal and pathological behavior. A growing number of studies indicate the involvement of the brain 5-HT system in the mechanisms underlying both ASD development and ASD-related behavioral disorders. There are some review papers describing the role of separate key players of the 5-HT system in an ASD and/or autistic-like behavior. In this review, we summarize existing data on the participation of all members of the brain 5-HT system, namely, 5-HT transporter, tryptophan hydroxylase 2, MAOA, and 5-HT receptors, in autism in human and various animal models. Additionally, we describe the most recent studies involving modern techniques for in vivo regulation of gene expression that are aimed at identifying exact roles of 5-HT receptors, MAOA, and 5-HT transporter in the mechanisms underlying autistic-like behavior. Altogether, results of multiple research articles show that the brain 5-HT system intimately partakes in the control of some types of ASD-related behavior, and that specific changes in a function of a certain 5-HT receptor, transporter, and/or enzyme may normalize this aberrant behavior. These data give hope that some of clinically used 5-HT-related drugs have potential for ASD treatment.

Schizophrenia in the genetic era: a review from development history, clinical features and genomic research approaches to insights of susceptibility genes

Schizophrenia is a devastating neuropsychiatric disorder affecting 1% of the world population and ranks as one of the disorders providing the most severe burden for society. Schizophrenia etiology remains obscure involving multi-risk factors, such as genetic, environmental, nutritional, and developmental factors. Complex interactions of genetic and environmental factors have been implicated in the etiology of schizophrenia. This review provides an overview of the historical origins, pathophysiological mechanisms, diagnosis, clinical symptoms and corresponding treatment of schizophrenia. In addition, as schizophrenia is a polygenic, genetic disorder caused by the combined action of multiple micro-effective genes, we further detail several approaches, such as candidate gene association study (CGAS) and genome-wide association study (GWAS), which are commonly used in schizophrenia genomics studies. A number of GWASs about schizophrenia have been performed with the hope to identify novel, consistent and influential risk genetic factors. Finally, some schizophrenia susceptibility genes have been identified and reported in recent years and their biological functions are also listed. This review may serve as a summary of past research on schizophrenia genomics and susceptibility genes (NRG1, DISC1, RELN, BDNF, MSI2), which may point the way to future schizophrenia genetics research. In addition, depending on the above discovery of susceptibility genes and their exact function, the development and application of antipsychotic drugs will be promoted in the future.

Transcranial ultrasound neuromodulation facilitates isoflurane-induced general anesthesia recovery and improves cognition in mice

Delayed arousal and cognitive dysfunction are common, especially in older patients after general anesthesia (GA). Elevating central nervous system serotonin (5-HT) levels can promote recovery from GA and increase synaptic plasticity to improve cognition. Ultrasound neuromodulation has become a noninvasive physical intervention therapy with high spatial resolution and penetration depth, which can modulate neuronal excitability to treat psychiatric and neurodegenerative diseases. This study aims to use ultrasound to noninvasively modulate the brain 5-HT levels of mice to promote recovery from GA and improve cognition in mice. The dorsal raphe nucleus (DRN) of mice during GA was stimulated by the 1.1 MHz ultrasound with a negative pressure of 356 kPa, and the liquid chromatography coupled tandem mass spectrometry (LC-MS/MS) method was used to measure the DRN 5-HT concentrations. The mice's recovery time from GA was assessed, and the cognition was evaluated through spontaneous alternation Y-maze and novel object recognition (NOR) tests. After ultrasound stimulation, the mice's DRN 5-HT levels were significantly increased (control: 554.0 ± 103.2 ng/g, anesthesia + US: 664.2 ± 84.1 ng/g, *p = 0.0389); the GA recovery time (return of the righting reflex (RORR) emergence latency time) of mice was significantly reduced (anesthesia: 331.6 ± 70 s, anesthesia + US: 223.2 ± 67.7 s, *p = 0.0215); the spontaneous rotation behavior score of mice was significantly increased (anesthesia: 59.46 ± 5.26 %, anesthesia + US: 68.55 ± 5.24 %; *p = 0.0126); the recognition index was significantly increased (anesthesia: 55.02 ± 6.23 %, anesthesia + US: 78.52 ± 12.21 %; ***p = 0.0009). This study indicates that ultrasound stimulation of DRN increases serotonin levels, accelerates recovery from anesthesia, and improves cognition, which could be an important strategy for treating delayed arousal, postoperative delirium, or even lasting cognitive dysfunction after GA.

Interplay of Cholesterol and Actin in Neurotransmitter GPCR Signaling: Insights from Chronic Cholesterol Depletion Using Statin

Serotonin1A receptors are important neurotransmitter receptors in the G protein-coupled receptor (GPCR) family and modulate a variety of neurological, behavioral, and cognitive functions. We recently showed that chronic cholesterol depletion by statins, potent inhibitors of HMG-CoA reductase (the rate-limiting enzyme in cholesterol biosynthesis), leads to polymerization of the actin cytoskeleton that alters lateral diffusion of serotonin1A receptors. However, cellular signaling by the serotonin1A receptor under chronic cholesterol depletion remains unexplored. In this work, we explored signaling by the serotonin1A receptor under statin-treated condition. We show that cAMP signaling by the receptor is reduced upon lovastatin treatment due to reduction in cholesterol as well as polymerization of the actin cytoskeleton. To the best of our knowledge, these results constitute the first report describing the effect of chronic cholesterol depletion on the signaling of a G protein-coupled neuronal receptor. An important message arising from these results is that it is prudent to include the contribution of actin polymerization while analyzing changes in membrane protein function due to chronic cholesterol depletion by statins. Notably, our results show that whereas actin polymerization acts as a negative regulator of cAMP signaling, cholesterol could act as a positive modulator. These results assume significance in view of reports highlighting symptoms of anxiety and depression in humans upon statin administration and the role of serotonin1A receptors in anxiety and depression. Overall, these results reveal a novel role of actin polymerization induced by chronic cholesterol depletion in modulating GPCR signaling, which could act as a potential therapeutic target.

Bio-enhanced fraction from Clitoria ternatea root extract ameliorates cognitive functions and in vivo hippocampal neuroplasticity in chronic cerebral hypoperfusion rat model

Research employing a bio-enhanced fraction of Clitoria ternatea (CT) to treat cognitive decline in the animal model has not yet been found. This study aimed to determine the neuroprotective effect of CT root bioactive fraction (CTRF) in chronic cerebral hypoperfusion (CCH) rat model. CTRF and its major compound, clitorienolactones A (CLA), were obtained using column chromatography. A validated HPLC-UV method was employed for the standardization of CTRF. CCH rats were given orally either vehicle or fraction (10, 20 and 40 mg/kg). Behavioural and hippocampal neuroplasticity studies were conducted following 4 weeks post-surgery. The brain hippocampus was extracted for proteins and neurotransmitters analyses. HPLC analysis showed that CTRF contained 25% (w/w) of CLA. All tested doses of CTRF and CLA (10 mg/kg) significantly restored cognitive deficits and reversed the inhibition of neuroplasticity by CCH. However, only CTRF (40 mg/kg) and CLA (10 mg/kg) significantly reversed the elevation of amyloid-beta plaque. Subsequently, treatment with CTRF (40 mg/kg) and CLA (10 mg/kg) alleviated the downregulation of molecular synaptic signalling proteins levels caused by CCH. The neurotransmitters level was restored following treatment of CTRF and CLA. Our finding suggested that CTRF improves memory and neuroplasticity in CCH rats which was mainly contributed by CLA.

Ameliorating the Role of Aripiprazole in Memory Deficits Induced by Intracerebroventricular Streptozotocin-Induced Dementia of Alzheimer's Type

Alzheimer's disease (AD) is a progressive neurodegenerative disorder causing immense suffering for the patients. Dopamine D2 and 5-hydroxytryptamine receptor 1A (5-HT1A) receptors' activation has been reported to play a crucial role in managing neurological outcomes in the brain and other health disorders. This study aimed to investigate the role of aripiprazole, a dopamine D2 and 5-HT1A selective receptors' activator, in the restoration of memory deficit induced by streptozotocin in mice. The cognitive functions of animals were determined using the Morris water maze. Brain sections were stained with hematoxylin and eosin and Congo red to examine the structural deviations. Brain oxidative stress (thiobarbituric acid reactive substance and glutathione), acetylcholinesterase activity, IL-6, and IL-10 were measured to assess biochemical alterations. Activation of D2 and 5-HT1A with aripiprazole attenuated STZ-induced cognitive deficit, increased brain GSH levels, reduced TBARS levels, AChE activity, IL-6 levels, and IL-10 levels and prevented STZ-induced brain anomalies in mice. Hence, the present study concluded that aripiprazole mitigated STZ-induced memory impairment and can be used as an efficacious therapeutic target for the management of AD.

Human tau-overexpressing mice recapitulate brainstem involvement and neuropsychiatric features of early Alzheimer's disease

Alzheimer's disease (AD) poses an ever-increasing public health concern as the population ages, affecting more than 6 million Americans. AD patients present with mood and sleep changes in the prodromal stages that may be partly driven by loss of monoaminergic neurons in the brainstem, but a causal relationship has not been firmly established. This is due in part to a dearth of animal models that recapitulate early AD neuropathology and symptoms. The goal of the present study was to evaluate depressive and anxiety-like behaviors in a mouse model of AD that overexpresses human wild-type tau (htau) prior to the onset of cognitive impairments and assess these behavior changes in relationship to tau pathology, neuroinflammation, and monoaminergic dysregulation in the dorsal raphe nucleus (DRN) and locus coeruleus (LC). We observed depressive-like behaviors at 4 months in both sexes and hyperlocomotion in male htau mice. Deficits in social interaction persisted at 6 months and were accompanied by an increase in anxiety-like behavior in males. The behavioral changes at 4 months coincided with a lower density of serotonergic (5-HT) neurons, downregulation of 5-HT markers, reduced excitability of 5-HT neurons, and hyperphosphorylated tau in the DRN. Inflammatory markers were also upregulated in the DRN along with protein kinases and transglutaminase 2, which may promote tau phosphorylation and aggregation. Loss of 5-HT innervation to the entorhinal cortex and dentate gyrus of the hippocampus was also observed and may have contributed to depressive-like behaviors. There was also reduced expression of noradrenergic markers in the LC along with elevated phospho-tau expression, but this did not translate to a functional change in neuronal excitability. In total, these results suggest that tau pathology in brainstem monoaminergic nuclei and the resulting loss of serotonergic and/or noradrenergic drive may underpin depressive- and anxiety-like behaviors in the early stages of AD.

On the role of serotonin 5-HT1A receptor in autistic-like behavior: сross talk of 5-HT and BDNF systems

Autism spectrum disorders (ASDs) are some of the most common neurodevelopmental disorders; however, the mechanisms underlying ASDs are still poorly understood. Serotonin (5-HT) and brain-derived neurotrophic factor (BDNF) are known as key players in brain and behavioral plasticity and interact with each other. 5-HT_1A receptor is a principal regulator of the brain 5-HT system, which modulates normal and pathological behavior. Here we investigated effects of adeno-associated-virus-based 5-HT_1A receptor overexpression in the hippocampus of BTBR mice (which are a model of autism) on various types of behavior and on the expression of 5-HT₇ receptor, proBDNF, mature BDNF, and BDNF receptors (TrkB and p75^NTR). The 5-HT_1A receptor overexpression in BTBR mice reduced stereotyped behavior in the marble-burying test and extended the time spent in the center in the open field test. Meanwhile, this overexpression failed to affect social behavior in the three-chambered test, immobility time in the tail suspension test, locomotor activity in the open field test, and associative learning within the "operant wall" paradigm. The 5-HT_1A receptor overexpression in the hippocampus raised hippocampal 5-HT₇ receptor mRNA and protein levels. Additionally, the 5-HT_1A receptor overexpression lowered both mRNA and protein levels of TrkB receptor but failed to affect proBDNF, mature BDNF, and p75^NTR receptor expression in the hippocampus of BTBR mice. Thus, obtained results suggest the involvement of the 5-HT and BDNF systems' interaction mediated by 5-HT_1A and TrkB receptors in the mechanisms underlying autistic-like behavior in BTBR mice.

Triiodothyronine Treatment reverses Depression-Like Behavior in a triple-transgenic animal model of Alzheimer's Disease

Alzheimer disease's (AD) is a neurodegenerative disorder characterized by cognitive and behavioral impairment. The central nervous system is an important target of thyroid hormones (TH). An inverse association between serum triiodothyronine (T3) levels and the risk of AD symptoms and progression has been reported. We investigated the effects of T3 treatment on the depression-like behavior in male transgenic 3xTg-AD mice. Animals were divided into 2 groups treated with daily intraperitoneal injections of 20 ng/g of body weight (b.w.) L-T3 (T3 group) or saline (vehicle, control group). The experimental protocol lasted 21 days, and behavioral tests were conducted on days 18-20. At the end of the experiment, the TH profile and hippocampal gene expression were evaluated. The T3-treated group significantly increased serum T3 and decreased thyroxine (T4) levels. When compared to control hippocampal samples, the T3 group exhibited attenuated glycogen synthase kinase-3 (GSK3), metalloproteinase 10 (ADAM10), amyloid-beta precursor-protein (APP), serotonin transporter (SERT), 5HT1A receptor, monocarboxylate transporter 8 (MCT8) and bone morphogenetic protein 7 (BMP-7) gene expression, whereas augmented superoxide dismutase 2 (SOD2) and Hairless gene expression. T3-treated animals also displayed reduced immobility time in both the tail suspension and forced swim tests, and in the latter presented a higher latency time compared to the control group. Therefore, our findings suggest that in an AD mouse model, T3 supplementation promotes improvements in depression-like behavior, through the modulation of the serotonergic related genes involved in the transmission mediated by 5HT1A receptors and serotonin reuptake, and attenuated disease progression.

Lysine 101 in the CRAC Motif in Transmembrane Helix 2 Confers Cholesterol-Induced Thermal Stability to the Serotonin1A Receptor

G protein-coupled receptors (GPCRs) constitute the largest class of membrane proteins that transduce signals across the plasma membrane and orchestrate a multitude of physiological processes within cells. The serotonin_1A receptor is a crucial neurotransmitter receptor in the GPCR family involved in a multitude of neurological, behavioral and cognitive functions. We have previously shown, using a combination of experimental and simulation approaches, that membrane cholesterol acts as a key regulator of organization, dynamics, signaling and endocytosis of the serotonin_1A receptor. In addition, we showed that membrane cholesterol stabilizes the serotonin_1A receptor against thermal deactivation. In the present work, we explored the molecular basis of cholesterol-induced thermal stability of the serotonin_1A receptor. For this, we explored the possible role of the K101 residue in a cholesterol recognition/interaction amino acid consensus (CRAC) motif in transmembrane helix 2 in conferring the thermal stability of the serotonin_1A receptor. Our results show that a mutation in the K101 residue leads to loss in thermal stability of the serotonin_1A receptor imparted by cholesterol, independent of membrane cholesterol content. We envision that our results could have potential implications in structural biological advancements of GPCRs and design of thermally stabilized receptors for drug development.

The dorsal hippocampal CA3 regulates spatial reference memory through the CtBP2/GluR2 pathway

The dorsal hippocampus plays a pivotal role in spatial memory. However, the role of subregion-specific molecular pathways in spatial cognition remains unclear. We observed that the transcriptional coregulator C-terminal binding protein 2 (CtBP2) presented CA3-specific enrichment in expression. RNAi interference of CtBP2 in the dorsal CA3 (dCA3) neurons, but not the ventral CA3 (vCA3), specifically impaired spatial reference memory and reduced the expression of GluR2, the calcium permeability determinant subunit of AMPA receptors. Application of an antagonist for GluR2-absent calcium permeable AMPA receptors rescued spatial memory deficits in dCA3 CtBP2 knockdown animals. Transcriptomic analysis suggest that CtBP2 may regulate GluR2 protein level through post-translational mechanisms, especially by the endocytosis pathway which regulates AMPA receptor sorting. Consistently, CtBP2 deficiency altered the mRNA expression of multiple endocytosis-regulatory genes, and CtBP2 knockdown in primary hippocampal neurons enhanced GluR2-containing AMPA receptor endocytosis. Together, our results provide evidence that the dCA3 regulates spatial reference memory by the CtBP2/GluR2 pathway through the modulation of calcium permeable AMPA receptors.

Cholesterol-Dependent Dynamics of the Serotonin1A Receptor Utilizing Single Particle Tracking: Analysis of Diffusion Modes

G protein-coupled receptors (GPCRs) are signaling hubs in cell membranes that regulate a wide range of physiological processes and are popular drug targets. Serotonin_1A receptors are important members of the GPCR family and are implicated in neuropsychiatric disorders. Cholesterol is a key constituent of higher eukaryotic membranes and is believed to contribute to the segregated distribution of membrane constituents into domains. To explore the role of cholesterol in lateral dynamics of GPCRs, we utilized single particle tracking (SPT) to monitor diffusion of serotonin_1A receptors under acute and chronic cholesterol-depleted conditions. Our results show that the short-term diffusion coefficient of the receptor decreases upon cholesterol depletion, irrespective of the method of cholesterol depletion. Analysis of SPT trajectories revealed that relative populations of receptors undergoing various modes of diffusion change upon cholesterol depletion. Notably, in cholesterol-depleted cells, we observed an increase in the confined population of the receptor accompanied by a reduction in diffusion coefficient for chronic cholesterol depletion. These results are supported by our recent work and present observations that show polymerization of G-actin in response to chronic cholesterol depletion. Taken together, our results bring out the interdependence of cholesterol and actin cytoskeleton in regulating diffusion of GPCRs in membranes.

The role of serotonin in declarative memory: A systematic review of animal and human research

The serotonergic system is involved in diverse cognitive functions including memory. Of particular importance to daily life are declarative memories that contain information about personal experiences, general facts, and events. Several psychiatric or neurological diseases, such as depression, attention-deficit-hyperactivity disorder (ADHD), and dementia, show alterations in serotonergic signalling and attendant memory disorders. Nevertheless, understanding serotonergic neurotransmission and its influence on memory remained a challenge until today. In this systematic review, we summarize recent psychopharmacological studies in animals and humans from a psychological memory perspective, in consideration of task-specific requirements. This approach has the advantage that comparisons between serotonin (5-HT)-related neurochemical mechanisms and manipulations are each addressing specific mnemonic circuits. We conclude that applications of the same 5-HT-related treatments can differentially affect unrelated tasks of declarative memories. Moreover, the analysis of specific mnemonic phases (e.g., encoding vs. consolidation) reveals opposing impacts of increased or decreased 5-HT tones, with low 5-HT supporting spatial encoding but impairing the consolidation of objects and verbal memories. Promising targets for protein synthesis-dependent consolidation enhancements include 5-HT₄ receptor agonists and 5-HT₆ receptor antagonists, with the latter being of special interest for the treatment of age-related decline. Further implications are pointed out as base for the development of novel therapeutic targets for memory impairment of neuropsychiatric disorders.

Antibiotic cocktail-induced gut microbiota depletion in different stages could cause host cognitive impairment and emotional disorders in adulthood in different manners

Gut microbiota depletion may result in cognitive impairment and emotional disorder. This study aimed to determine the possible association between host gut microbiota, cognitive function, and emotion in various life stages and its related underlying mechanisms. Seventy-five neonatal mice were randomly divided into five groups (n = 15 per group). Mice in the vehicle group were administered distilled water from birth to death, and those in the last four groups were administered antibiotic cocktail from birth to death, from birth to postnatal day (PND) 21 (infancy), from PND 21 to 56 (adolescence), and from PND 57 to 84 (adulthood), respectively. Antibiotic exposure consistently altered the gut microbiota composition and decreased the diversity of gut microbiota. Proteobacteria were the predominant bacteria instead of Firmicutes and Bacteroidetes after antibiotic exposure in different life stages. Long-term and infant gut microbiota depletion resulted in anxiety- and depression-like behaviors, memory impairments, and increased expression of γ-aminobutyric acid type A receptor α1 of adult mice. Long-term antibiotic exposure also significantly decreased serum interleukin (IL)-1β, IL-10, and corticosterone of adult mice. Gut microbiota depletion in adolescence resulted in anxiety-like behaviors, short-term memory decline, decreased serum interferon-γ (IFN-γ), mRNA expression of 5-hydroxytryptamine receptor 1A, and neuropeptide Y receptor Y2 in the prefrontal cortex of adult mice. Antibiotic exposure in adulthood damaged short-term memory and decreased serum IL-10, IFN-γ, and increased γ-aminobutyric acid type B receptor 1 mRNA expression of adult mice. These results suggest that antibiotic-induced gut microbiota depletion in the long term and infancy resulted in the most severe cognitive and emotional disorders followed by depletion in adolescence and adulthood. These results also suggest that gut microbes could influence host cognitive function and emotion in a life stage-dependent manner by affecting the function of the immune system, hypothalamic-pituitary-adrenal axis, and the expression of neurochemicals in the brain.

Behavioral Training Related Neurotransmitter Receptor Expression Dynamics in the Nidopallium Caudolaterale and the Hippocampal Formation of Pigeons

Learning and memory are linked to dynamic changes at the level of synapses in brain areas that are involved in cognitive tasks. For example, changes in neurotransmitter receptors are prerequisite for tuning signals along local circuits and long-range networks. However, it is still unclear how a series of learning events promotes plasticity within the system of neurotransmitter receptors and their subunits to shape information processing at the neuronal level. Therefore, we investigated the expression of different glutamatergic NMDA (GRIN) and AMPA (GRIA) receptor subunits, the GABAergic GABARG2 subunit, dopaminergic DRD1, serotonergic 5HTR1A and noradrenergic ADRA1A receptors in the pigeon’s brain. We studied the nidopallium caudolaterale, the avian analogue of the prefrontal cortex, and the hippocampal formation, after training the birds in a rewarded stimulus-response association (SR) task and in a simultaneous-matching-to-sample (SMTS) task. The results show that receptor expression changed differentially after behavioral training compared to an untrained control group. In the nidopallium caudolaterale, GRIN2B, GRIA3, GRIA4, DRD1D, and ADRA1A receptor expression was altered after SR training and remained constantly decreased after the SMTS training protocol, while GRIA2 and DRD1A decreased only under the SR condition. In the hippocampal formation, GRIN2B decreased and GABARG2 receptor expression increased after SR training. After SMTS sessions, GRIN2B remained decreased, GABARG2 remained increased if compared to the control group. None of the investigated receptors differed directly between both conditions, although differentially altered. The changes in both regions mostly occur in favor of the stimulus response task. Thus, the present data provide evidence that neurotransmitter receptor expression dynamics play a role in the avian prefrontal cortex and the hippocampal formation for behavioral training and is uniquely, regionally and functionally associated to cognitive processes including learning and memory.

Associations Between a Polymorphism in the Rat 5-HT1A Receptor Gene Promoter Region (rs198585630) and Cognitive Alterations Induced by Microwave Exposure

The nervous system is a sensitive target of electromagnetic radiation (EMR). Chronic microwave exposure can induce cognitive deficits, and 5-HT system is involved in this effect. Genetic polymorphisms lead to individual differences. In this study, we evaluated whether the single-nucleotide polymorphism (SNP) rs198585630 of 5-HT_1A receptor is associated with cognitive alterations in rats after microwave exposure with a frequency of 2.856 GHz and an average power density of 30 mW/cm². Rats were exposed to microwaves for 6 min three times a week for up to 6 weeks. PC12 cells and 293T cells were exposed to microwaves for 5 min up to 3 times at 2 intervals of 5 min. Transcriptional activity of 5-HT_1A receptor promoter containing rs198585630 C/T allele was determined in vitro. Electroencephalograms (EEGs), spatial learning and memory, and mRNA and protein expression of 5-HT_1A receptor were evaluated in vivo. We demonstrated that transcriptional activity of 5-HT_1A receptor promoter containing rs198585630 C allele was higher than that of 5-HT_1A receptor promoter containing T allele. The transcriptional activity of 5-HT_1A receptor promoter was stimulated by 30 mW/cm² microwave exposure, and rs198585630 C allele was more sensitive to microwave exposure, as it showed stronger transcriptional activation. Rats carrying rs198585630 C allele exhibited increased mRNA and protein expression of 5-HT_1A receptor and were more susceptible to 30 mW/cm² microwave exposure, showing cognitive deficits and inhibition of brain electrical activity. These findings suggest SNP rs198585630 of the 5-HT_1A receptor is an important target for further research exploring the mechanisms of hypersensitivity to microwave exposure.

Cannabidiol and the corticoraphe circuit in post-traumatic stress disorder

Post-Traumatic Stress Disorder (PTSD), characterized by re-experiencing, avoidance, negative affect, and impaired memory processing, may develop after traumatic events. PTSD is complicated by impaired plasticity and medial prefrontal cortex (mPFC) activity, hyperactivity of the amygdala, and impaired fear extinction. Cannabidiol (CBD) is a promising candidate for treatment due to its multimodal action that enhances plasticity and calms hyperexcitability. CBD’s mechanism in the mPFC of PTSD patients has been explored extensively, but literature on the mechanism in the dorsal raphe nucleus (DRN) is lacking. Following the PRISMA guidelines, we examined current literature regarding CBD in PTSD and overlapping symptomologies to propose a mechanism by which CBD treats PTSD via corticoraphe circuit. Acute CBD inhibits excess 5-HT release from DRN to amygdala and releases anandamide (AEA) onto amygdala inputs. By first reducing amygdala and DRN hyperactivity, CBD begins to ameliorate activity disparity between mPFC and amygdala. Chronic CBD recruits the mPFC, creating harmonious corticoraphe signaling. DRN releases enough 5-HT to ameliorate mPFC hypoactivity, while the mPFC continuously excites DRN 5-HT neurons via glutamate. Meanwhile, AEA regulates corticoraphe activity to stabilize signaling. AEA prevents DRN GABAergic interneurons from inhibiting 5-HT release so the DRN can assist the mPFC in overcoming its hypoactivity. DRN-mediated restoration of mPFC activity underlies CBD’s mechanism on fear extinction and learning of stress coping.

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CBD reduces PTSD symptoms via the DRN and corticoraphe circuit.

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Acute effects of CBD reduce DRN-amygdala excitatory signaling to lessen the activity disparity between amygdala and mPFC.

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Chronic CBD officially resolves mPFC hypoactivity by facilitating 5-HT release from DRN to mPFC.

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CBD-facilitated endocannabinoid signaling stabilizes DRN activity and restores mPFC inhibitory control.

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Chronically administered CBD acts via the corticoraphe circuit to favor fear extinction over fear memory reconsolidation.

The selective 5-HT1A receptor biased agonists, F15599 and F13714, show antidepressant-like properties after a single administration in the mouse model of unpredictable chronic mild stress

RATIONALE

The prevalence of depression is ever-increasing throughout the population. However, available treatments are ineffective in around one-third of patients and there is a need for more effective and safer drugs.

OBJECTIVES

The antidepressant-like and procognitive effects of the "biased agonists" F15599 (also known as NLX-101) which preferentially targets postsynaptic 5-HT1A receptors and F13714, which targets 5-HT1A autoreceptors, were investigated in mice.

METHODS

Antidepressant-like properties of the compounds and their effect on cognitive functions were assessed using the forced swim test (FST) and the novel object recognition (NOR), respectively. Next, we induced a depressive-like state by an unpredictable chronic mild stress (UCMS) procedure to test the compounds' activity in the depression model, followed by measures of sucrose preference, FST, and locomotor activity. Levels of phosphorylated cyclic AMP response element-binding protein (p-CREB) and phosphorylated extracellular signal-regulated kinase (p-ERK1/2) were also determined.

RESULTS

F15599 reduced immobility time in the FST over a wider dose-range (2 to 16 mg/kg po) than F13714 (2 and 4 mg/kg po), suggesting accentuated antidepressant-like properties in mice. F15599 did not disrupt long-term memory consolidation in the NOR at any dose tested, while F13714 impaired memory formation, notably at higher doses (4-16 mg/kg). In UCMS mice, a single administration of F15599 and F13714 was sufficient to robustly normalize depressive-like behavior in the FST but did not rescue disrupted sucrose preference. Both F15599 and F13714 rescued cortical and hippocampal deficits in p-ERK1/2 levels of UCMS mice but did not influence the p-CREB levels.

CONCLUSIONS

Our studies showed that 5-HT1A receptor biased agonists such as F13714 and especially F15599, due to its less pronounced side effects, might have potential as fast-acting antidepressants.

The contributions of entorhinal cortex and hippocampus to error driven learning

Computational models proposed that the medial temporal lobe (MTL) contributes importantly to error-driven learning, though little direct in-vivo evidence for this hypothesis exists. To test this, we recorded in the entorhinal cortex (EC) and hippocampus (HPC) as macaques performed an associative learning task using an error-driven learning strategy, defined as better performance after error relative to correct trials. Error-detection signals were more prominent in the EC relative to HPC. Early in learning hippocampal but not EC neurons signaled error-driven learning by increasing their population stimulus-selectivity following error trials. This same pattern was not seen in another task where error-driven learning was not used. After learning, different populations of cells in both the EC and HPC signaled long-term memory of newly learned associations with enhanced stimulus-selective responses. These results suggest prominent but differential contributions of EC and HPC to learning from errors and a particularly important role of the EC in error-detection.

Ku et al. recorded in the entorhinal cortex (EC) and hippocampus (HPC) of macaques during associative learning tasks in order to test the computational model prediction that they contribute to error-driven learning. They demonstrate that the EC and HPC have prominent but differential contributions to learning from errors, with the EC having a particularly prominent role in error-detection.

Neural substrates involved in the cognitive information processing in teleost fish

Over the last few decades, it has been shown that fish, comprising the largest group of vertebrates and in many respects one of the least well studied, possess many cognitive abilities comparable to those of birds and mammals. Despite a plethora of behavioural studies assessing cognition abilities and an abundance of neuroanatomical studies, only few studies have aimed to or in fact identified the neural substrates involved in the processing of cognitive information. In this review, an overview of the currently available studies addressing the joint research topics of cognitive behaviour and neuroscience in teleosts (and elasmobranchs wherever possible) is provided, primarily focusing on two fundamentally different but complementary approaches, i.e. ablation studies and Immediate Early Gene (IEG) analyses. More recently, the latter technique has become one of the most promising methods to visualize neuronal populations activated in specific brain areas, both during a variety of cognitive as well as non-cognition-related tasks. While IEG studies may be more elegant and potentially easier to conduct, only lesion studies can help researchers find out what information animals can learn or recall prior to and following ablation of a particular brain area.

Effect of tertiary amine local anesthetics on G protein-coupled receptor lateral diffusion and actin cytoskeletal reorganization

Although widely used clinically, the mechanism underlying the action of local anesthetics remains elusive. Direct interaction of anesthetics with membrane proteins and modulation of membrane physical properties by anesthetics are plausible mechanisms proposed, although a combination of these two mechanisms cannot be ruled out. In this context, the role of G protein-coupled receptors (GPCRs) in local anesthetic action is a relatively new area of research. We show here that representative tertiary amine local anesthetics induce a reduction in two-dimensional diffusion coefficient of the serotonin_1A receptor, an important neurotransmitter GPCR. The corresponding change in mobile fraction is varied, with tetracaine exhibiting the maximum reduction in mobile fraction, whereas the change in mobile fraction for other local anesthetics was not appreciable. These results are supported by quantitation of cellular F-actin, using a confocal microscopic approach previously developed by us, which showed that a pronounced increase in F-actin level was induced by tetracaine. These results provide a novel perspective on the action of local anesthetics in terms of GPCR lateral diffusion and actin cytoskeleton reorganization.

Exploring the impact of trauma type and extent of exposure on posttraumatic alterations in 5-HT1A expression

The long-term behavioral, psychological, and neurobiological effects of exposure to potentially traumatic events vary within the human population. Studies conducted on trauma-exposed human subjects suggest that differences in trauma type and extent of exposure combine to affect development, maintenance, and treatment of a variety of psychiatric syndromes. The serotonin 1-A receptor (5-HT1A) is an inhibitory G protein-coupled serotonin receptor encoded by the HTR1A gene that plays a role in regulating serotonin release, physiological stress responding, and emotional behavior. Studies from the preclinical and human literature suggest that dysfunctional expression of 5-HT1A is associated with a multitude of psychiatric symptoms commonly seen in trauma-exposed individuals. Here, we synthesize the literature, including numerous preclinical studies, examining differences in alterations in 5-HT1A expression following trauma exposure. Collectively, these findings suggest that the impact of trauma exposure on 5-HT1A expression is dependent, in part, on trauma type and extent of exposure. Furthermore, preclinical and human studies suggest that this observation likely applies to additional molecular targets and may help explain variation in trauma-induced changes in behavior and treatment responsivity. In order to understand the neurobiological impact of trauma, including the impact on 5-HT1A expression, it is crucial to consider both trauma type and extent of exposure.

G-Protein-Coupled Receptors in CNS: A Potential Therapeutic Target for Intervention in Neurodegenerative Disorders and Associated Cognitive Deficits

Neurodegenerative diseases are a large group of neurological disorders with diverse etiological and pathological phenomena. However, current therapeutics rely mostly on symptomatic relief while failing to target the underlying disease pathobiology. G-protein-coupled receptors (GPCRs) are one of the most frequently targeted receptors for developing novel therapeutics for central nervous system (CNS) disorders. Many currently available antipsychotic therapeutics also act as either antagonists or agonists of different GPCRs. Therefore, GPCR-based drug development is spreading widely to regulate neurodegeneration and associated cognitive deficits through the modulation of canonical and noncanonical signals. Here, GPCRs’ role in the pathophysiology of different neurodegenerative disease progressions and cognitive deficits has been highlighted, and an emphasis has been placed on the current pharmacological developments with GPCRs to provide an insight into a potential therapeutic target in the treatment of neurodegeneration.

Effect of heat-inactivated Lactobacillus paracasei N1115 on microbiota and gut-brain axis related molecules

This study was conducted to evaluate the possibility of using heated-inactivated lactobacilli to protect neonates from harmful effects of antibiotics. Thirty neonate mice were randomly divided into three groups of ten and treated with either sterilized water, an antibiotics cocktail, or the same antibiotics plus heat-inactivated Lactobacillus paracasei N1115. The administration of antibiotics significantly increased the serum interleukin-6 (IL-6) levels of the tested mice (p<0.01, p<0.001, respectively) and decreased their serum corticosterone levels (p<0.01, p<0.01, respectively). The colonic crypts were significantly less deep in mice treated with antibiotics and with antibiotics plus N1115 (p<0.05). Antibiotics caused significantly abnormal expression of brain-derived neurotrophic factor (BDNF), γ-aminobutyric acid type A receptor α1 (GABA_Aα1), γ-aminobutyric acid type B receptor1 (GABA_b1), and 5-hydroxytryptamine receptor1A (5-HT_1A) in the hippocampus (p<0.05, p<0.01, p<0.01, respectively) and of GABA_Aα1 in the prefrontal cortex (p<0.01). Heat-inactivated lactobacilli alleviated these abnormal changes. Antibiotics greatly decreased the Shannon index of the fecal microbiota and significantly increased the number of Proteobacteria (p<0.001), with fewer Bacteroidetes and Firmicutes (p<0.05). Antibiotics not only cause microbiota dysbiosis, but also cause abnormal changes in important molecules in the gut-brain axis. All these abnormal changes are alleviated by heat-inactivated L. paracasei N1115. This indicates that heat-inactivated L. paracasei N1115 has a certain improvement effect on changes caused by antibiotics.

The serotonin system in the hippocampus CA3 involves in effects of CSDS on social recognition in adult female mandarin voles (Microtus mandarinus)

Chronic social defeat stress (CSDS) exacerbated the development of stress-related psychiatric disorders, and the social recognition dysfunction is the core feature of many psychiatric disorders. However, the effects of CSDS on female social recognition and the underlying neural mechanisms remain unclear. Using highly aggressive adult female mandarin voles (Microtus mandarinus) as animal model, the aim of this work is to investigate the effects of CSDS on social recognition in adult female rodents and the neurobiological mechanisms underlying these effects. Our results indicate the CSDS disrupted the normal social recognition in adult female voles. Meanwhile, defeated voles exhibited increased neural activity in the DG, CA1 and CA3 of the hippocampus. Furthermore, CSDS reduced levels of serotonin (5-HT) and serotonin 1A receptors (5-HT_1AR) in the CA3. We also discovered that microinjection of 8-OH-DPAT into the CA3 effectively reversed the social recognition deficits induced by CSDS, and an infusion of WAY-100635 into the CA3 of control female voles impaired social recognition. Moreover, targeted activation of the 5-HT neuron projection from the DRN to CA3 by long-term administration of CNO significantly prevented the CSDS induced social recognition deficits. Taken together, our study demonstrated that CSDS induced social recognition deficits in adult female voles, and these effects were mediated by the action of 5-HT on the 5-HT_1AR in the hippocampus CA3. The projection from the DRN to CA3 may be involved in social recognition deficits induced by CSDS.

The 5-hydroxytryptamine 2A receptor agonists DOI and 25CN-NBOH decrease marble burying and reverse 8-OH-DPAT-induced deficit in spontaneous alternation

5-Hydroxytryptamine 2A receptor (5-HT_2AR) agonist psychedelics are increasingly recognized as potentially useful treatments of psychiatric disorders, such as obsessive-compulsive disorder, depression, anxiety, and drug dependence. There is limited understanding of the way they exert their therapeutic action, but inhibition of rigid behavior and cognition has been suggested as a key factor. To examine the role of 5-HT_2ARs in modulating repetitive behavior, we tested two 5-HT_2AR agonists, DOI, and the selective 25CN-NBOH, in two mouse tests of compulsive-like behavior. Using adult C57BL/6JOlaHsd male mice, we examined the effects of the two compounds on digging behavior in the marble burying test and on 8-OH-DPAT-disrupted spontaneous alternation behavior in the Y-maze. Both compounds dose-dependently decreased digging behavior in the marble burying test, indicating anti-compulsivity effects, which were not related to non-specific locomotor inhibition. Both 5-HT_2AR agonists also reversed 8-OH-DPAT-reduced alternation ratio in the spontaneous alternation behavior test, although the effects were less pronounced than in the marble burying test. This suggests that the 5-HT_2AR promotes exploratory behavior, but that the deficit produced by 8-OH-DPAT is too excessive to be fully reversed by 5-HT_2AR agonists. This study shows that agonism of 5-HT_2AR reduces repetitive behavioral patterns, supporting the theory that this is a potential new treatment approach to disorders of cognitive or behavioral inflexibility. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Embelin Improves the Spatial Memory and Hippocampal Long-Term Potentiation in a Rat Model of Chronic Cerebral Hypoperfusion

Alzheimer's disease (AD) is the second most occurring neurological disorder after stroke and is associated with cerebral hypoperfusion, possibly contributing to cognitive impairment. In the present study, neuroprotective and anti-AD effects of embelin were evaluated in chronic cerebral hypoperfusion (CCH) rat model using permanent bilateral common carotid artery occlusion (BCCAO) method. Rats were administered with embelin at doses of 0.3, 0.6 or 1.2 mg/kg (i.p) on day 14 post-surgery and tested in Morris water maze (MWM) followed by electrophysiological recordings to access cognitive abilities and synaptic plasticity. The hippocampal brain regions were extracted for gene expression and neurotransmitters analysis. Treatment with embelin at the doses of 0.3 and 0.6 mg/kg significantly reversed the spatial memory impairment induced by CCH in rats. Embelin treatment has significantly protected synaptic plasticity impairment as assessed by hippocampal long-term potentiation (LTP) test. The mechanism of this study demonstrated that embelin treatment alleviated the decreased expression of BDNF, CREB1, APP, Mapt, SOD1 and NFκB mRNA levels caused by CCH rats. Furthermore, treatment with embelin demonstrated neuromodulatory activity by its ability to restore hippocampal neurotransmitters. Overall these data suggest that embelin improve memory and synaptic plasticity impairment in CCH rats and can be a potential drug candidate for neurodegenerative disease-related cognitive disorders.

Role of Actin Cytoskeleton in Dynamics and Function of the Serotonin1A Receptor

G protein-coupled receptors (GPCRs) are important membrane proteins in higher eukaryotes that carry out a vast array of cellular signaling and act as major drug targets. The serotonin_1A receptor is a prototypical member of the GPCR family and is implicated in neuropsychiatric disorders such as anxiety and depression, besides serving as an important drug target. With an overall goal of exploring the functional consequence of altered receptor dynamics, in this work, we probed the role of the actin cytoskeleton in the dynamics, ligand binding, and signaling of the serotonin_1A receptor. We monitored receptor dynamics utilizing single particle tracking, which provides information on relative distribution of receptors in various diffusion modes in addition to diffusion coefficient. We show here that the short-term diffusion coefficient of the receptor increases upon actin destabilization by cytochalasin D. In addition, analysis of individual trajectories shows that there are changes in relative populations of receptors undergoing various types of diffusion upon actin destabilization. The release of dynamic constraint was evident by an increase in the radius of confinement of the receptor upon actin destabilization. The functional implication of such actin destabilization was manifested as an increase in specific agonist binding and downstream signaling, monitored by measuring reduction in cellular cAMP levels. These results bring out the interdependence of GPCR dynamics with cellular signaling.

8-OH-DPAT Induces Compulsive-like Deficit in Spontaneous Alternation Behavior: Reversal by MDMA but Not Citalopram

Rodents exhibit natural exploratory behaviors, which can be measured by the spontaneous alternation behavior (SAB) test. Perseverance in this test induced by the 5-hydroxytryptamine 1A receptor (5-HT_1AR) agonist, 8-hydroxy-2-dipropylaminotetralin (8-OH-DPAT), resembles compulsive behaviors observed in humans and manifests as reduced alternation ratio. This study characterized 8-OH-DPAT-induced perseverance in the SAB test in C57BL/6JOlaHsd male mice by coadministration of WAY100635, citalopram and the 5-HT releasing agent, 3,4-methylenedioxymethamphetamine (MDMA), to deepen the understanding of 5-HT-dependent mechanisms. The 5-HT_1AR mechanism of 8-OH-DPAT (1.0 mg/kg, p < 0.01) on perseverance was confirmed by coadministration of the 5-HT_1AR antagonist, WAY100635 (2.0 mg/kg, p < 0.05), which attenuated the effects of 8-OH-DPAT. Such effects could also be reversed by MDMA (1.0 mg/kg, p < 0.05; 10.0 mg/kg, p < 0.001) but not citalopram. These findings confirm the importance of 5-HT in regulating perseverative behavior. Future investigations are required to determine the predictive validity of the 8-OH-DPAT-disrupted SAB test as an inducible mouse model of compulsivity.

Alterations in serotonin transporter and body image-related cognition in anorexia nervosa

The serotonin system has been implicated in the pathophysiology of anorexia nervosa (AN). A recent report proposed that body image distortion (BID), a core symptom of AN, may relate to abnormalities of the serotonin system, especially the serotonin transporter (5HTT). Positron emission tomography (PET) studies of underweight patients with active AN reported alterations in serotonin receptors, but not 5HTT. Here, we aimed to disclose the clinicopathophysiology of AN by focusing on 5HTT and cognitive functions, including BID, in groups with active AN. Twenty-two underweight female patients with AN (12 restricting-type AN (ANR); 10 binge-eating/purging-type AN (ANBP)) and 20 age-matched healthy female subjects underwent PET with a 5HTT radioligand [¹¹C]DASB. The binding potential (BP_ND) of [¹¹C]DASB was estimated semiquantitatively, and clinical data from Raven's colored progressive matrices for general intelligence, the Stroop test for focused attention, the Iowa gambling task for decision making and a dot-probe task designed for BID were compared with the levels of BP_ND in different groups. [¹¹C]DASB BP_ND was significantly decreased in the medial parietal cortex in patients with AN and in the dorsal raphe in patients with ANR compared with healthy subjects (p < .05 corrected). Patients with ANR showed a significantly negative correlation between [¹¹C]DASB BP_ND in the dorsal raphe and performance on the dot-probe task (p < .05 corrected). While reduced 5HTT in the medial parietal cortex (the somatosensory association area) is pathophysiologically important in AN in general, additional 5HTT reduction in the dorsal raphe as seen in ANR is implicated for the clinicopathophysiological relevance.

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5HTT decreased in the parietal cortex in patients with AN.

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5HTT decreased in the parietal cortex in patients with ANBP.

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5HTT decreased in the parietal cortex and the dorsal raphe in patients with ANR.

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Patients with AN were poor at responding to the test for body image distortion (BID).

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5HTT in the dorsal raphe was associated with cognitive performance of BID.

Serotonergic system, cognition, and BPSD in Alzheimer's disease

Behavioral and Psychological Symptoms of Dementia (BPSD), present in almost 90% of patients with Alzheimer's Disease (AD), cause extensive impairment leading to reduced independence and inability to complete activities of daily living. Though BPSD includes a wide range of symptoms, such as agitation, aggression, disinhibition, anxiety, depression, apathy, delusions, and hallucinations. Certain BPSD in AD co-present and can be clustered into distinct domains based on their frequency of co-occurrence. As these BPSD are so pervasive in any stages of AD, the disease may be better characterized as a disorder of heterogeneous degenerative symptoms across a number of symptom domains, with the most prominent domain comprising memory and cognitive deficits. Importantly, there are no FDA-approved drugs to treat these BPSD, and new approaches must be considered to develop effective treatments for AD patients. The biogenic monoamine 5-hydroxytryptamine (5-HT), or serotonin, works as both a neurotransmitter and neuromodulator, which has been tied to cognitive decline and multiple BPSD domains. This review summarizes the evidence for specific serotonergic system alterations across some of the well-studied cognitive, behavioral, and psychiatric domains. Though differences in overall serotonergic transmission occur in AD, circuit-specific alterations in individual 5-HT receptors (5-HTRs) are likely linked to the heterogeneous presentation of BPSD in AD.

Intrahippocampal 5-HT1A receptor antagonist inhibits the improving effect of low-frequency stimulation on memory impairment in kindled rats

In addition to its anticonvulsant effect, low frequency stimulation (LFS) improves learning and memory in kindled animals. In the present study, the role of 5-HT_1A receptors in mediating LFS' improving effect on spatial learning and memory was investigated in amygdala-kindled rats. Amygdala kindling was conducted in a semi-rapid kindling stimulations (12 stimulations per day) in male Wistar rats. LFS (4 trains of 0.1 ms pulse duration at 1 Hz, 200 pulses, 50-150 μA, at 5 min intervals) was applied after termination of kindling stimulations. NAD-299 (a selective 5-HT_1A receptor antagonist; 2.5 and 5 μg/μl) was microinjected into the hippocampal CA1 before applying LFS. The Morris water maze, and novel object recognition tests were conducted after the last kindling stimulation. Hippocampal samples were also prepared, and 5-HT_1A receptor gene expression levels were assessed using quantitative RT-PCR. In kindled animals, LFS reduced impairments in spatial learning and memory in the Morris water maze and novel object recognition tests. Microinjection of NAD doses of 5 μg/μl reduced the effects of LFS on learning and memory. The gene expression level of 5-HT_1A receptors increased significantly in the hippocampus of amygdala-kindled rats. However, LFS applied after kindling stimulations inhibited this effect. It seems that activation of 5-HT_1A receptors in the CA1 field is necessary for LFS' improving effects on spatial learning and memory in kindled animals; although surprisingly, LFS application prevented the elevation in gene expression of 5-HT_1A receptors in kindled animals.

Acute Cannabinoids Produce Robust Anxiety-Like and Locomotor Effects in Mice, but Long-Term Consequences Are Age- and Sex-Dependent

The rise in cannabinoid legalization and decriminalization in the US has been paired with an increase in adolescents that perceive marijuana as a “no risk” drug. However, a comprehensive review of human literature indicates that cannabinoid usage may have both beneficial and detrimental effects, with adolescent exposure being a critical window for harming cognitive development. Although the cannabinoids Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) are often used together for recreational and medical purposes, no study has previously observed the acute and long-lasting effects of THC+CBD in a battery of behavioral assays analogous to subjective human reports. The current study observed the acute and long-term effects of THC, CBD, and THC+CBD on object recognition memory, anxiety-like behavior, and activity levels in adolescent and adult mice of both sexes. Acute THC alone and in combination with CBD resulted in robust effects on anxiety-like and locomotor behavior. A history of repeated cannabinoid treatment followed by a period without drug administration resulted in minimal effects in these behavioral assays. Most notably, the strongest effects of repeated cannabinoid treatment were seen in adult females administered THC+CBD, which significantly impaired their object recognition. No effects of repeated cannabinoid history were present on hippocampal protein expression. These studies represent a detailed examination of age- and sex-effects of acute and repeated cannabinoid administration. However, the acute and long-term effects of THC with and without CBD on additional behaviors in adolescents and adults will need to be examined for a more complete picture of these drug effects.

Study of the Effects of L-tryptophane Nanoparticles on Motor Behavior in Alzheimer's Experimental Models

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disease characterized by the progressive and incapacitating decay of cognitive, neuropsychiatric, and behavioral manifestations. L-tryptophan is the precursor amino acid of serotonin, which is a neurotransmitter responsible for mood balance and the sense of well-being and can be administered in the form of nanoparticles.

OBJECTIVE

This study analyzed the effectiveness of L-tryptophan nanoparticles and L-tryptophan on behavioral physiological alterations resulting from AD in animal models.

METHODS

The sample consisted of 50 Rattus norvegicus rats, divided in 10 groups with 5 animals each: one negative control (NC), three positive control groups (C3, C7, and C21), three groups treated with L-tryptophan nanoparticles (T3N, T7N, and T21N) at the concentration of 1.5 mg, and three groups treated with L-tryptophan (T3L, T7L, and T21L) at the concentration of 1.5 mg. The rats underwent stereotactic surgery to induce AD through the injection of amyloid beta-amyloid peptide1-42 in the intracerebroventricular region. All rats were submitted to pre- and post-surgery and post-treatment motor behavior evaluation through the Later Water Maze (LWM) and elevated cross-labyrinth (ECL). Histological analysis was performed to verify the presence of senile plaques, and the statistical analysis used the unpaired T-test.

RESULTS

Significant intergroup differences were observed in some of the evaluated parameters between treated and untreated groups.

CONCLUSION

It was concluded that the treatment with L-tryptophan nanoparticles was beneficial to improve behavioral reactions in the Alzheimer's model.

Dose related effects of buspirone on pain, learning / memory and food intake

The present study concerned extending the therapeutic use of buspirone for treating pain and improving cognition. Effects of single and repeated administration of buspirone were therefore monitored on pain threshold in the hot plate test and on spatial memory in the water maze test in rats. Effects on cumulative food intake were also monitored. The drug was administered intraperitoneally in doses of 0.1, 0.3, 1.0 and 2.0 mg/kg. We found that single and repeated administration of buspirone in doses of 0.1 mg/kg decreased pain threshold in the hot plate test, while doses of 1.0 and 2.0 mg/kg increased it. Effects of single and repeated administration were not different. A dose of 0.3 mg/kg had no effect. Food intake increased following single as well as repeated administration of 0.1 mg/kg buspirone; higher doses had no effect. Low doses (0.1 and 0.3 mg/kg) improved acquisition and retention of memory in the water maze test, while memory extinction was reduced. Higher doses had either no effect (1.0 mg/kg) or impaired (2.0 mg/kg) performance in this test. The results suggest potential therapeutic use of selected doses of buspirone as an analgesic and nootropic drug.